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Even Identical Twins Have Different DNA

For years the dogma was that identical twins possessed DNA profiles that were not distinguishable from one another. But things are changing.

Fraternal (dizygotic) twins come from two eggs and two sperm and are as different as if born years apart. They are twins solely because they shared the mother’s womb at the same time. But, identical twins (monozygotic) come from a single egg and sperm. They are formed when the fertilized egg undergoes its first division and the two new daughter cells move apart, each then proceeding to form a separate individual. Since they came from the same fertilized egg, the share the same DNA. In fact, the two would be indistinguishable by standard PCR-STR DNA Profiling.

 

Twins

 

But, in reality, even identical twins have distinct DNA. We just weren’t able to see the differences. Before now.

As each twin embryo grows and develops in utero, and the cells continue to multiply, the replication (copying) of each twin’s DNA isn’t perfect. Minor errors or variations begin to appear so that by birth each Twin’s DNA is slightly different from its sibling. And as life goes on, each twin is subjected to different environmental stresses, which is turn alters each one’s DNA replication.

As opposed to STR, which looks at repeating short sequences of bases within the DNA strand, a newer DNA technique, known as Single Nucleotide Polymorphism (SNP), gives the examiner a complete DNA sequence of the strand being analyzed. That is the exact sequence of bases in each strand is determined and this can reveal the differences in the DNA of identical twins. Another newer technique known as High Resolution Melt Curve Analysis (HRMA) might offer still another method to make this distinction.

So even identical twins are not so identical.

Want to know more about DNA profiling? Check out the updated 2nd Edition of FORENSICS FOR DUMMIES.

 

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Posted by on May 2, 2016 in DNA, Uncategorized

 

The Cyber Exchange Principle

Dr. Edmond Locard

Dr. Edmond Locard

 

The cornerstone of forensic science is known as the Locard Exchange Principle. Edmond Locard (1877-1966) studied and developed his investigative skills under the great forensic pioneer Alexandre Lacassagne and later headed the forensic laboratory in Lyon, France. His observations led him to conclude that criminals always left traces of themselves at crime scenes. And took evidence away when they departed. This became the foundation of his exchange principle.

 

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FROM FORENSICS FOR DUMMIES, 2nd EDITION:

The Cornerstone of Forensic Science: Locard’s Exchange Principle

Every contact you make with another person, place, or object results in an exchange of physical materials. If you own a pet, this material exchange is well known to you. Look at your clothes and you’re likely to see cat or dog hair clinging to the fabric—a pain in the behind if you want to keep your clothes looking sharp, but an incredible boon for forensic science. You may also find that you transfer these hairs to your car, your office, and any other place you frequent.

Known as the Locard Exchange Principle, after Dr. Edmond Locard, the French police officer who first noticed it, the exchange of materials is the basis of modern forensic investigation. Using this principle, forensic scientists can determine where a suspect has been by analyzing trace evidence (any small piece of evidence), such as fibers on clothing, hair in a car, or gunk on the soles of shoes.

Looking at Locard’s principle in action:

As an example, say that you have two children and a cat. You run out to take care of some errands that include stopping at a furniture store, the laundry, and the house of a friend who has one child and a dog. From a forensic science standpoint, this sequence of events can provide a gold mine of information.

You leave behind a little bit of yourself at each stop, including

* Hair from yourself, your children, and your cat

* Fibers from your clothing and the carpets and furniture in your home and

car

* Fingerprints and shoe prints

* Dirt and plant matter from your shoes

* Biological materials, if you accidentally cut yourself and leave a drop of

blood on the floor or sneeze into a tissue and then drop it in a trash can

But that’s not all. You also pick up similar materials everywhere you go:

* Fibers from each sofa or chair you sat on at the furniture store ride away

on your clothes, as do hair and fibers left behind by customers who sat

there before you.

* Fibers of all types flow through the air and ventilation system and settle on

each customer at the laundry.

* Hair from your friend, her child, and her dog latch on to you as do fibers

from your friend’s carpet and furniture.

* Fibers, hairs, dirt, dust, plant material, and gravel are collected by your

shoes and pants everywhere you set foot.

In short, by merely running errands, you become a walking trace evidence

factory.

Today, many crimes have at least some cyber component—cell phones, computers, e mails. text messages, etc. Does the cyber world also have such a cyber exchange principle? Yes it does and it’s actually quite extensive.

Forensic Magazine article: http://www.forensicmag.com/articles/2011/12/digital-forensics-cyber-exchange-principle#.UtFmzHn4VTE

 
2 Comments

Posted by on April 12, 2016 in Uncategorized

 

Guest Blogger: Megan Inslee: My Love-Hate Relationship with Forensic DNA

dna_rgb

 

What is the most important point to keep in mind when working with forensic DNA evidence?  There are probably a lot of answers to that question, depending on your experience and perspective.  I’ll let you in on my opinion for now, as a former DNA forensic scientist. One of the imperatives of working forensic DNA cases in this modern age is this: accepting that there are cases (many, in fact) that DNA can’t resolve.

Almost every time I testify, I’m asked “why might you not find DNA?” This is a good question, one which I usually answer with a fairly long list of possibilities, but it all boils down to three main points. 1. DNA may not have been deposited in the first place. Does this mean that the incident didn’t happen as reported by the victim or witnesses? Not necessarily – more on that a bit later.   2. Maybe too little DNA was deposited for the lab to test and identify. But can’t you guys detect even a few cells? More on that, later, too.  Or, 3. Perhaps DNA was deposited at an adequate level, but much of it was washed away or degraded over time. I saw a special on cold cases solved by DNA decades later – I don’t believe there’s anything you can’t do. Well, keep reading.

1. DNA may not have been deposited in the first place.

We’ve become so accustomed to DNA evidence being presented in criminal justice cases that we seem to need to take a collective step back to reflect on a case in which it just isn’t there.  It really depends on the scenario and the knowns of the case what this lack of DNA on an evidence item could mean.

The murderer doesn’t always cut herself on the knife and leave drops of her blood at the scene. The burglar may have kept his gloves on throughout the entire crime, never touching anything with a bare hand.  A child molester doesn’t always leave semen evidence for us to test.

And, of course, DNA may not be present on a tested evidence item simply because the scenario didn’t unfold the way investigators believed or the witnesses stated or the victim recalled.  Corroborating DNA evidence with reported scenarios is a tricky business, one which doesn’t always result in a resolution tied up with a big red bow.

2. Maybe too little DNA was deposited for the lab to test and identify.

Remember the days when crime labs couldn’t get DNA from anything smaller than a blood drop the size of a quarter?  And remember when, even when they started getting DNA from smaller samples, the odds of someone else having the same DNA profile was only one in several thousand?  Well, I don’t – that was before my time.

But I was there for the early years of the current DNA typing technology, Short Tandem Repeats (STRs). Those were the days in which we tested mainly blood, semen, and saliva.  We had a good idea of what we could and couldn’t get results from and we ended up with a lot of single-source DNA profiles.  These result in straight forward comparisons to reference samples which yield either an exclusion, if the profiles don’t match, or a match.  In the case of a match, we calculate and issue some crazy-big statistic that illustrates to the reader (the investigator or attorney or juror) just how significant this match is (spoiler alert: the number is often in the quadrillions – matches are pretty darn significant).  And as great as this is and was, the criminal justice system wanted (and in many cases, needed) more.

Science over time, I’ve found, rarely disappoints.  The techniques and products that result from years of experimentation, trial and error, grant funding and academic research end up being a culmination of the best approach among many.

Instead of changing the sites we used for forensic DNA typing, researchers found that we could extract and clean up the DNA a little better and attain higher sensitivity.  They modified the primers and added a few more.  They improved the reagents that we used to get our profiles and made them a little more robust. They made instruments that could automate sample processing so that we could do more samples in less time.  All of this has led to higher throughput and more sensitive results.

Currently, scientists are not just attempting to get DNA profiles from well-defined body fluid stains, as before, but also from areas of evidence items that have tested faintly positive for a body fluid. They are swabbing areas of items that someone in the case may have touched.  These types of samples have much, much fewer cells than, say, a fat drop of blood.  And, while significant to the case and incident at hand, these samples are likely to contain not only very few cells, but mixtures of more than one person’s DNA, further complicating the analysis.

3. Perhaps DNA was deposited at an adequate level, but much of it was washed away or degraded over time. 

It’s important to remember that DNA is a molecule, one with millions of parts.  Cells must be intact in order to properly preserve the DNA.  And hundreds of cells must be present in a sample in order to obtain a decent profile for comparison. Wiping or washing a surface can remove cells. Environmental factors such as heat, UV light, or bacteria can break cells open, exposing DNA and ultimately breaking it down.

Also, it’s useful to know that the laboratory process, itself, is lengthy, requiring many phases, none of which perfectly preserve all of the DNA in the sample from one step to the next.  If I detect 200 cells in a sample in the lab, it doesn’t mean that 200 cells were originally deposited on the evidence item at the time of the crime.  Even in the best evidence-preservation scenario, there is loss of genetic material on the crime-scene-through-laboratory-testing journey.

In the end, as much as I love forensic DNA (and I hope you do, too), it’s important to keep its limitations in perspective in every case. The presence of DNA evidence does not prove guilt. The absence of DNA evidence does not prove innocence. The current state of forensic DNA technology is, however, amazing! I think we can all relish in that without abandoning our role as critical thinkers.

MInslee

Megan Inslee spent 13 years as a DNA forensic scientist in Washington State.  She has her Bachelor’s in Biology as well as her Master’s in the Genetics track of Laboratory Medicine from the University of Washington. She currently resides on an island outside of Seattle with her husband and three small children, writing technical documents, preparing grant proposals, and providing consultation on a freelance basis.

 
4 Comments

Posted by on March 29, 2016 in DNA, Guest Blogger, Uncategorized

 

Dirty DNA

microfluidic

 

One truth in forensic DNA testing is that you must have a sample to test. That, of course, should be self-evident. But sometimes crime scene DNA isn’t readily available. There are no blood or semen stains on the floor or bed sheets or any location where they could be easily sampled. What’s the crime lab to do?

New methods are under development that allow for extracting useable DNA from some unusual places, even dirt. GEMBE (gradient elution moving boundary electrophoresis) grabs DNA hidden in the dirt by employing a molecular “tug-of-war.” Cool.

For more about DNA sampling and testing, grab a copy of my updated, 2nd Edition of FORENSICS FOR DUMMIES.

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INFO/PURCHASE

 

Crime and Science Radio: Crime and Science in the OC: an Interview with Bruce Houlihan, Director of the Orange County Crime Lab

Houlihan

BIO: Bruce Houlihan is Director of the Orange County Crime Lab in Santa Ana, California, and has been with the County of Orange for 29 years. He spent much of his childhood living in Tokyo, Japan, and also Southern California where he was born. After completing an undergraduate degree in chemistry and physics, he spent a year doing graduate study in chemistry at the University of California, Irvine, and another two years of graduate leadership study at Vanguard University in Costa Mesa. He has taught chemistry and physics at Vanguard University as a part-time adjunct for many years while working for the Sheriff-Coroner as a forensic scientist (formerly known as criminalists). After being hired in the mid 1980’s, he began work in the forensic chemistry areas, specifically toxicology and controlled substance analysis. He served as the president of the California Association of Crime Laboratory Directors, is a member of the American Society of Crime Lab Directors, and is currently participating with NIST on the Organization of Scientific Area Committees during the current national dialog in forensics. Mr. Houlihan serves at one of the largest crime labs in the country, with over 130 forensic specialists, forensic scientists, and support staff. He lives with his family in Orange County, and in his spare time enjoys reading, creative thinking, and puzzles.

LISTEN: http://www.blogtalkradio.com/suspensemagazine/2015/12/15/crime-and-science-radio-with-special-guest-bruce-houlihan

Link will go live Saturday February 13, 2016 at 10 a.m. Pacific

LINKS:

Orange County Sheriff-Coroner Department – Orange County Crime Lab http://www.occl.ocgov.com

Orange County Sheriff’s Department – http://ocsd.org

American Society of Crime Laboratory Directors http://www.ascld.org

American Academy of Forensic Sciences http://www.aafs.org

California Association of Criminalists http://www.cacnews.org

 

Edgar Mitchell, the 6th Man to Walk on the Moon, Dies

Edgar Mitchell

Astronaut Edgar Mitchell

This is sad. Only 12 men have set foot on the moon and Edgar was the 6th. As Apollo 14’s Lunar Module pilot, his main job was to transport himself and fellow astronaut Alan Shepard to the moon’s surface and back to the Command Module safely. He easily did so. Apollo 14 was an especially tense trip after the near disaster of Apollo 13.

 

MItchell on Moon

Edgar Mitchell on the Moon

A few years ago I was invited by NASA’s Marshall Space Flight Center to do the ribbon cutting for the opening of CSI: The Experience at the Space Museum in Huntsville, AL—my hometown. Marshall is very engaged in developing new and improved forensic science techniques and equipment.

It was a very special experience, particularly for a boy who grew up with Von Braun’s rocket boosters periodically shaking the ground and building rockets in my backyard. At the reception, which was held at the Davidson Center For Space Exploration, I met Edgar. He was an intelligent and witty man. So long, Edgar, you are a national hero.

 

Space Museum Night copy

Space Museum Huntsville, AL

Davidson Center

Davidson Center for Space Exploration

 
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Posted by on February 6, 2016 in Space Program, Uncategorized

 

Crime and Science Radio: Tracking Down the Bad Guys: A Conversation with Retired US Marshal and Novelist Marc Cameron

Join Jan Burke and me as we welcome retire US Marshal Marc Cameron and discuss how the Marshals track down the bad guys—from Texas to Alaska. It’s a great show. Don’t miss it.

BIO: Marc Cameron is a retired Chief Deputy US Marshal and 29-year law enforcement veteran. His short stories have appeared in BOYS’ LIFE Magazine and the Saturday Evening Post. He’s published eleven novels, six of them Westerns.

BRUTE FORCE, sixth in his USA Today Bestselling Jericho Quinn Thriller series, is available December 2016 from Kensington. A second degree black belt in Ju Jitsu, Marc teaches defensive tactics to law enforcement agencies and civilian groups.

He lives in Alaska with his beautiful bride and BMW motorcycle.

 

Alaska Tracking Unit

 

Tracking in AZ

LISTENhttp://www.blogtalkradio.com/suspensemagazine/2016/01/16/crime-and-science-radio-with-special-guest-marc-cameron

LINKS:

Marc Cameroon Website: http://www.marccameronbooks.com

Marc Cameron on Facebook: https://www.facebook.com/MarcCameronAuthor

Marc Cameron Blog: http://www.marccameronbooks.com/blog.htm

US Marshals Service: http://www.usmarshals.gov

 

Brute Force

 

Day Zero

 
 
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